In the protection technologies for the Ethernet ring network, multiple nodes are connected to each other to constitute a ring, and a section of link on the ring is defined as a ring protection link. When the state of each link on the ring has no failure, the ring protection link is blocked and the service communication data between the nodes can not pass through the ring protection link, thereby preventing a “broadcast storm” caused by a closed ring, and any two nodes on the ring only have therebetween one path capable of communicating. In general, the port of a node being blocked means that the port can not forward service communication data when it is set blocked, and the port being unblocked means that the port can forward the service communication data when it is set unblocked, wherein whether the port is blocked or unblocked does not affect the forwarding of a protocol frame protected by an Ethernet ring, unless it is especially pointed out that the port blocks or unblocks the forwarding function of the protocol frame protected by the Ethernet ring. A link being blocked means that one of the two adjacent ports of the link is blocked or both of the two ports are blocked, and the service data can not be forwarded through one of the two adjacent ports of the link and thus the service data can not pass through the blocked link; and a link being unblocked means that both of the two adjacent ports of the link are unblocked, and thus the service data can be forwarded through the two adjacent ports of the link.
When a link on the ring fails, and if the failed link is not the ring protection link, the ring protection link is unblocked. Since the path of the service communication data is changed, the nodes on the ring need to update a FDB (Forwarding Database), and the service communication data between the nodes can pass through the ring protection link and is transmitted through the new path and thus is reconnected, and further a new FDB is learned and established. When the failed link on the ring is recovered, the ring protection link is re-blocked, the service communication data can not be transmitted via the ring protection link, the transmission path of the service communication data will also be changed and the nodes on the ring also need to update the FDB.
Taking RFC3619 as an example, one node on the ring is defined as a master node (MASTER) (the master node is also called as a ring protection link affiliation node), and the other nodes are defined as transit nodes (TRANSIT); the two ports on the ring of the mater node are respectively defined as a master port (P) and a slave port (S), and when the state of each link on the ring has no failure, the master node blocks the service communication data of the slave port. As shown in FIG. 1a, the node S2 is a master node, the other nodes are transit nodes; the port 2 of the node S2 is a master port and the port 1 is a slave port, and when the states of the links on the ring are in good condition, the master node S2 blocks the service communication data of the slave port 1, which means that the link between the nodes S2 and S4 is a ring protection link, thereby preventing a closed ring in the network, and user 1 and user 2 only have one communication path therebetween. When a link on the ring fails, the adjacent ports of the failing link notify the master node that a link on the ring fails, and the master node unblocks the slave port, updates the FDB, and notifies other nodes to update the FDB too, and after the other nodes update the FDB upon receiving the notification, the service communication between the nodes is transmitted according to the new path. As shown in FIG. 1b, the link between the node S3 and the node S4 fails, and the nodes S3 and S4 notify the master node S2 that the link on the ring fails, the master node unblocks the slave port, i.e., unblocks the ring protection link, updates the FDB and sends a protocol frame (Flush-Down) to notify other nodes to update the FDB; transmission is performed according to the new path after the nodes update the FDB, and the service data between the user 1 and the user 2 is reconnected. When the failed link on the ring is recovered, the slave port of the master node is re-blocked, the service communication data can not be transmitted via the slave port of the master node, and the transmission path of the service communication data will also be changed, the master node needs to update the FDB itself and also needs to notify the other nodes on the ring to update the FDB.
When an Ethernet ring network protection system conducts switching, the original path is changed, there is false MAC address egress port information in the FDB of the nodes, and thus the FDB needs to be updated so that the service data can be transmitted through a new path. Before the nodes update the FDB, there is a false table item in the FDB, and if a data frame finds a false egress port according to the FDB of the nodes, it can not reach the target node, and thus the data frame will be lost; after the nodes update the FDB, the original FDB table item on the nodes are cleared up, the data frame can not find the egress port corresponding to the target MAC address, then it is broadcasted to each port so as to reach the target node; when receiving the data frame, a node learn the MAC address in the frame and establishes a new FDB. In general, it is time consuming for a node to update the FDB, and before a new FDB is established, the broadcasting of the data frame can easily block the links so that the service data communication is interrupted for a long time and the nodes receive a lot of irrelevant frames which leads to a too heavy instantaneous burden of the whole system.